It's a miracle that this second sequel to a giant of the sci-fi genre manages to overcome its could-be-Carry On opening sequence; top level military types, having retrieved their space shuttle from the Pacific Ocean, express dismay when the three astronauts remove their helmets, revealing that its astronauts are of course chimpanzees. Keep an eye out for M Emmet Walsh doing a remarkable yet unintentional Phil Silvers-as-Sgt Bilko impression.
Fortunately, with the requisite suspension of disbelief, things do improve, and the story explores a human population accepting and embracing talking apes. It's a rather clever twist (achieving the not inconsiderable task of producing a follow-on from 'Beneath's rather conclusive finale, but only just), providing enough room to explore a decent idea on another shrunken budget. It does dissolve into a somewhat predictable ending - possibly because this was the first in the series to be written with the possibility of further instalments in mind – but at least retains some of the pessimistic foreboding of its predecessors.